Assessing Insect Dynamics in the Sour Rot Disease Etiology of Grapes

View the project final report

Commodities

• Fruits: grapes

Practices

• Pest Management: integrated pest management

Sour rot is an economically important disease in vineyards in wet and humid regions. The disease symptoms cause a reduction in productivity and the commercial quality of grapes. It is challenging to manage sour rot sustainably as it involves a tripartite interaction among microorganisms (bacteria and yeast), insects such as Drosophila fruit flies, and grape berries plus the abiotic environment. This study aims to understand the role of insects in sour rot development in grapes. Here, we propose to:

1. Assess Drosophila melanogaster behavior, the species of fruit fly most commonly associated with sour rot, in response to olfactory cues produced from microbe-inoculated and non-inoculated berries.
2. Determine whether infestation by the invasive fruit fly Drosophila suzukii facilitates subsequent infestation by Drosophila melanogaster and sour rot disease.
3. Assess whether yellow jacket and grape berry moth damage to berries interact synergistically with Drosophila fruit flies to increase sour rot disease.

We hypothesize that distinctive odors emitted by microbe-inoculated berries drive sour rot – Drosophila interactions.  We expect that D. suzukii facilitates infestation by D. melanogaster and the degree of facilitation is time-dependent. We hypothesize damage to berries from grape berry moths and yellow jackets interacts synergistically with Drosophila fruit flies to increase sour rot. If successful, this study will elucidate the role of multiple insects in sour rot etiology and provide new insights into sustainable disease management strategies. The results will be extended to stakeholders and the scientific community through presentations at conferences, newsletter articles, and peer-reviewed publications.

1. Understand the role of odors in mediating interactions between sour rot and Drosophila

1A. Assess D. melanogaster behavior in response to odors produced from inoculated and non-inoculated berries

We hypothesize that sour rot-associated microbes alter the volatile composition of berry tissue and thus alter D. melanogaster behavior. We will inoculate grapes with a sour rot-associated microbes and conduct choice bioassays to observe the behavior of D. melanogaster over time. We will also evaluate D. melanogaster preference for odors from treated berries with and without larvae.

1B. Assess volatile profiles of inoculated and non-inoculated berries

We hypothesize that disease associated microbes alter berry odors that D. melanogaster uses to distinguish amongst berries. We will collect volatiles from berries inoculated with yeast and bacteria with or without larvae in laboratory assays and conduct volatile analysis using GCMS. These data will provide insights into possible changes in the volatile profile of berries associated with differences in behavior uncovered in objective 1A.

2. Evaluate whether suzukii infestation facilitates subsequent D. melanogaster infestation

2A. Quantify D. melanogaster behavior when provided with berries with larvae or probing marks by D. suzukii

D. suzukii is active in vineyards earlier than D. melanogaster as they prefer to lay eggs in ripening and ripe berries. We hypothesize that this early berry damage caused by D. suzukii activity allows D. melanogaster to lay eggs in fruit more easily, thereby aggravating sour rot risk. We will evaluate whether D. suzukii activity affect the foraging and oviposition of D. melanogaster through video-recordings of fly behaviors.

2B. Evaluate facilitation of D. melanogaster by D. suzukii in berries and its impact on sour rot incidence and severity in the field

We will specifically test whether injuries and cues left by D. suzukii at different time points increase the likelihood that D. melanogaster lays eggs and how that differentially affects sour rot development in field trial.

3. Assess whether damage from yellow jackets and grape berry moth (GBM) interacts with Drosophila and sour rot development

 As grapes ripen, yellow jackets forage on berries for sugars and pulp. GBM larvae feed inside berries during late summer. We hypothesize a synergistic interaction occurs amongst yellow jackets and GBM berry damage, Drosophila flies, and microbes, causing increased sour rot disease. We will conduct a field trial with enclosed grape clusters in mesh bags to manipulate the presence of D. melanogaster, GBM, yellow jackets, and causal microbes.